U.S. Pat. No. 3,832,499 (Oscar Heil) discloses an electro-acoustic transducer in which a conductor is arranged in a meander pattern on at least one side of a flexible diaphragm, such that the current in adjacent conductive strands flows in opposite directions. The flexible diaphragm is pleated or corrugated in a suitable jig such that when the corrugated diaphragm is placed in a magnetic field oriented in a front to rear axis with electrical current flowing perpendicular to the magnetic field in one direction in a given fold and in an opposite direction in an adjacent fold, the adjacent folds are alternately displaced to the right and to the left along the third perpendicular axis. The air spaces between adjacent folds facing one side of the diaphragm are expanded while the air spaces on the other side are contracted. After the pleats have been formed, the assembly is tempered and affixed at either end. The finished corrugated unit is then cemented inside a plastic frame thereby forming an assembly which may be inserted and removed from a slotted space inside a magnetic structure. As the Heil patent indicates, having two sets of conductors, one on each side of the diaphragm, doubles the force. Additional embodiments may have two or more conductive strands arranged adjacently on each half pleat on a single side of the diaphragm.
A two-part article in Speaker Builder (March and April 1982) by Kenneth Rauen discloses alternate designs for the diaphragm of a horn loaded "Heil Air Motion Transformer" ("AMT"), based in part on techniques previously published by Neil Davis (Audio Amateur, February 1977), in which a razor blade was used to cut the meandering conductor from a 1 mil layer of aluminum foil. In one embodiment the meandering conductor was sandwiched between two 1 mil layers of polyethylene with rubber cement. In another embodiment, the meandering conductor was fastened to a 0.5 mil layer of polyethylene and covered with a vinyl coating. Stiffeners at either end of the diaphragm were epoxied into aluminum frames, and a screw operated tension block at one end of the frame was used to slightly stretch the diaphragm after the epoxy had set (but not to the point where the diaphragm was "noticeably taut").
Another, presently preferred, AMT design is described and claimed in an unpublished commonly assigned PCT application entitled IMPROVED HORN LOADED PLEATED RIBBON HIGH FREQUENCY ACOUSTIC TRANSDUCER WITH SUBSTANTIALLY UNIFORM COUPLING, filed on Nov. 6, 1997 and hereby incorporated in its entirety by reference.